This invention relates to lubricating oil compositions and more particularly to polyisobutylene succinimide dispersants, ethylene-propylene succinimide antioxidant-dispersants and alkylated phenothiazine antioxidants for single grade and multigrade lubricating oil compositions.
Internal combustion engines operate under a wide range of temperatures including low temperature stop-and-go service as well as high temperature conditions produced by continuous high speed driving. Stop-and-go driving, particularly during cold, damp weather conditions, leads to the formation of sludge in the crankcase and in the oil passages of a gasoline or a diesel engine. This sludge seriously limits the ability of the crankcase oil to effectively lubricate the engine. In addition, the sludge with its entrapped water tends to contribute to rust formation in the engine. These problems tend to be aggravated by the manufacturer's lubrication service recommendations which specify extended oil drain intervals.
It is known to employ nitrogen containing dispersants and/or detergents in the formulation of crankcase lubricating oil compositions. Many of the known dispersant/detergent compounds are based on the reaction of an alkenylsuccinic acid or anhydride with an amine or polyamine to produce an alkylsuccinimide or an alkenylsuccinamic acid as determined by selected conditions of reaction.
Also it is known to chlorinate alkenylsuccinic acid or anhydride prior to the reaction with an amine or polyamine in order to produce a reaction product in which a portion of the amine or polyamine is attached directly to the alkenyl radical of the alkenyl succinic acid or anhydride. The thrust of many of these processes is to produce a product having a relatively high level of nitrogen in order to provide improved dispersancy in a crankcase lubricating oil composition.
With the introduction of four cylinder internal combustion engines which must operate at relatively higher engine speeds or RPM's than conventional 6-and 8-cylinder engines in order to produce the required torque output, it has become increasingly difficult to provide a satisfactory dispersant anti-oxidant lubricating oil composition.
Recessive valve train wear, piston deposits, and oil thickening can occur at high engine operating temperatures with poorly formulated lubricating oils. Valve train wear and piston deposits can cause engine malfunction and in some cases result in engine failure. Excessive oxidative oil thickening can prevent the oil from flowing to the engine's oil pump causing the engine to seize due to lack of lubrication.
The conventional sludge dispersants for lubricating oils have been of the polyisobutenyl succinimide (PIBSAD) type for over 20 years. Recent changes in test procedures have made it more difficult to qualify these types of dispersants for use in lubricating oils without substantially increasing their treating dosage. The novel lubricating oil composition of the invention contains two different dispersants, they are low molecular weight ethylene-propylene succinimides (LEPSAD) and PIBSAD dispersants (described in numerous patents).
Together with alkylated phenothiazines (described in numerous patents) they exhibit an unexpected improvement in ASTM Sequence IIIE gasoline engine test ratings than any of these components can provide separately. This unexpected improvement in Sequence IIIE rating is a unique and useful example of synergism between different components in a lubricating oil formulation.
Thus, it is an object of the present invention to provide an effective dispersant, anti-oxidant additive for single-grade and multigrade lubricating oils.